Trapezius
Like the sternocleidomastoid, the trapezius is a compound muscle consisting of three distinct parts, as indicated by a more or less clear separation of the clavicular portion of the muscle from the rest and, less frequently, by the separation of the lower from the middle portion. The three parts consist of
- A dorsoscapularis superior,
- A dorsoscapularis inferior, and
- A a cleidooccipitalis division. Occasionally, bundles pass from the anterior border of the clavicular portion of trapezius to join the cleidooccipitalis portion of sternocleidomastoideus, indicating perhaps a common origin of the two muscles.
Variations likewise occur in the extent of the spinal attachments of trapezius, owing to the the reduction of one or another of its parts; this attachment usually extends lower in the muscle on the right side than in that on the left. In a study of the lower limit in origin of the trapezius muscle Mori reports the following for 108 Japanese cadavers or 216 sides:
Note the asymmetry of origin. It has been reported that asymmetry of origin of the trapezius muscle occurs in about 20-25% of individuals.
The trapezius may send a fascicle to the sternum and to the deltoid muscle. Mori has pointed out that the trapezius develops from the branchial musculature. The anlaga for trapezius and sternocleidomastoid separates with the ventral part forming sternocleidomastoid and the dorsal part forming trapezius. Not infrequently, both muscles extend for a greater distance than usual along the clavicle. In many of these cases, the external jugular passes through a space in the anterior expansion of the trapezius. The space for the vein arises from the clavicle and a space or split in the muscle or in a tendinous component of the muscle. The origin of the two muscles provides clues as to the types of variations to be found. Knowledge of human embryology is a valuable asset in understanding human anatomic variation in this region.
A rare muscle, supraclavicularis proprius, may be found adjacent and superficial to trapezius. Supraclavicularis proprius consists of an anterior sheet inserting on the clavicle with the trapezius and a posterior sheet inserting into fascia colli superficialis. This muscle arises from the sternum and sternal end of the clavicle, and may insert into the fascia of the dorsal scapular region as well as into those areas cited above.
Supernumerary clavicular muscles are numerous but uncommon. They include:sternoclavicularis anticus (also referred to as praesternoclavicularis mediale, coracoclavicularis singularis, acromioclavicularis or preclavicularis lateralis), supraclavicularis proprius (tensor laminae superficialis fasiale colli), and retroclavicularis proprius (tensor laminae profundus fasciale colli). Dorsofascialis, another sheet of the panniculus carnosus, has been reported superficial to trapezius.
A bundle of fibers (omocervicalis, omotrachelien, or levator claviculae) may lie beneath the cervical portion of trapezius. It attaches distally to the lateral end of the clavicle or to the acromion, and originates above from transverse processes of some of the upper cervical vertebrae, usually the atlas and axis. It occurs in about 2% of cases.
Trachleoclavicularis imus (Gruber) is a small supernumerary muscle extending between the clavicle and the transverse process of the sixth cervical vertebra. Another small muscle, omoclavicularis, joins the scapula and clavicle. This muscle arises from the superior margin of the beneath (or ventral to) the omohyoid muscle and extends by a narrowing muscle mass and tendon to insert onto the inner surface of the middle of the clavicle. Mori found this muscle in 6 sides of 200 cadaver sides ( or about 3%).
The bilateral and unilateral absence of trapezius has been noticed. The muscle's origin may not ascend above the axis or descend below the third thoracic vertebra.
Syn.: m. cucullaris (Henle), Kappenmuskel, Mönchskappenmuskel, Scarf muscle, Cowl muscle.
References
Ato, T. and E. Gi. (1959) One case of the M. clavicularis posteror. Jinruigaku, Jinruiidengaku, Taishitsugaku Ronbumshu 38:45-47. In Japanese.
Beaton, L.E. and B.J. Anson. (1942) Variations in the origin of the m. trapezius. Anat. Rec. 83:41-46.
Calori, L. (1866) Intorno ad alcune varietè incontrate nella muscolatura degli arti superiori annotazioni anatomiche. Mem. R. Accad. Sci. Istituto di Bologna S. 2 6:137147
Corner, E.M. (1901) Proceedings of the Anatomical Society of Great Britian and Ireland, June, 1900. A communication of a case of omo-trachelian muscle in a living subject. J. Anat. Physiol. 35:iii.
Gruber, W. (1873) Sur un muscle cleido-hyoidien et sur un muscle supraclaviculaire singulier chez l'homme. Bull. de l'Acad. Imp. des Sci. de St. Petersbourg 18:154-157.
Gruber, W. (1884) Neuer Musculus retro-clavicularis proprius- tensor laminae profundae fascia colli. Arch. Path. Anat. Physiol. Klin. Med. 98:416-422.
von Haffner, H. (1903) Eine seltene doppelseitige Anomalie des Trapezius. Internat. Monatsschrift für Anat. Physiol. 20:313-318.
Hirohashi, A., Hayashi, K., and H. Akimoto. (1958) One case of anomaly of the M. trapezius. Kurume Igakkai Zasshi 21 :992-996. In Japanese.
Kariya, K. (1936) One case of the variation of the M. trapezius approaching to the whole absence. Hokuetsu Igakkai Zasshi 51:1139-1142. In Japanese.
Kredel, L. (1900) Ueber angeborene Halsmuskeldefecte. ??????? 56:398-406. z Deutsche Med. Wochenschrift.
Komiya, R. Yoshimura, H. and K. Honkoku. (1955) On the anomalies of the insertion of the M. trapezius. Kurume Igakkai Zasshi 18:1042-1044. In Japanese.
Laidlaw, P.P. (1902) A supraclavicularis proprius (Gruber). J. Anat. Physiol. 36:417418
Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series), with a catalogue of the principal musclular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-134.
Mori, M. (1940) Observations on the M. Trapezius and the M. pectoralis minor. Igaku Kenkyu 14:85-88. In Japanese.
Mori, M. (1964) Statistics on the musculature of the Japanese. Okajimas Fol. Anat. Jap. 40:195-300.
Mori,-. and -. Minoru. (1949) Studies on the musculature of the back of the fetus, especially comparative studies on it of the twin-fetus, on the M. trapezius. Kaibogaku Zasshi 24:109. In Japanese.
Oyama, M. (1957) One case of the reduced origin of the M. trapezius. Tokyo Jikeikai Ikadaigaku Zasshi 72:1011-1013. In Japanese
Perrin, J.B. (1871) A rudiment of the dorsal portion of the panniculus carnosus, superficial to the trapezius. J. Anat. Physiol. 5:251-256.
Rutherford, N. (1910) A curious arrangement of the retroclavicular musculature. Anat. Anz. 37:148-150.
Selden, B.R. (1935) Congenital absence of trapezius and rhomboideus major muscles. J. Bone Joint Surg. 17:1058-1059.
Sheehan, D. (1932) Bilateral absence of trapezius. J. Anat. 67:180-181.
Stange, P. (1896) Ueber einen Fall von fast vollstanigem Defekt des rechten Musculus cucullaris und des rechten Musculus sternocleidomastoideus. Deutsche Medicinische Wochenschrift 22:412-414.
Tsuda, M. (1939) Supernumerous muscle-bundle of the Mm. infrahyoidei and M. trapezius. Iwate Igakusenmongakko Zasshi. 3:186-189. In Japanese.
Vastarini-Cresi, G. (1906) Nouvelle variètè de musculus supraclavicularis chez l'homme et sa signification probable. Arch. Ital. Biol. 46:290-291.
Yamada, F. (1934) Some variations of the infrahyoidal muscles and insertion of the trapezius into the clavicula. Kaibogaku Zasshi 7:337-347. In Japanese.